This invention relates to a method and apparatus for measuring the stiffness of materials utilized as structural members or the like.
The bending stiffness, for example, of a test piece of such material is generally obtained by multiplying the Young's modulus of the material and the moment of inertia I of the test piece. With recent development of synthetic materials and such compound structures as sandwich structures, it is the recent trend to express the strength of the material in terms the bending stiffness B instead of troublesome method involving the measurement of the Young's modulus and the calculation of the moment of inertia I.
Heretobefore, the bending stiffness B has been measured by means of an Amsler type universal testing machine. More particularly, taking a typical three point bending mode as an example, the opposite ends of a simple beam 1 are supported on sharp supports or fulcrums 2 and a concentrated load W is applied to the center of the beam 1 as shown in FIG. 1. The relationship between the maximum deflection .delta. and the bending stiffness B=E.multidot.I under these conditions is expressed by the following equation EQU .delta.=Wl.sup.3 /48E.multidot.I
where l represents the distance or span between the supports. Accordingly, in this testing machine it is necessary to mount the supports 2 on a rigid bed or a surface plate 3 so that the testing machine is not only heavy but also expensive. According to the method of measuring bending stiffness described above, since the bending stiffness B is determined as a function of three independent variables that is deflection .delta., weight W and span l it has been impossible to obtain a testing machine providing a direct reading of the bending stiffness.